An excavator, which is a construction machine performing an excavating operation for digging in the ground at a civil engineering site, a building site, and a construction site, a loading operation of transporting earth and sand, a crushing operation for braking a structure, a tillage operation for organizing the ground, and the like, is formed of a front attachment including a travelling body serving to move equipment, an upper turning body mounted on the travelling body and rotated 360°, a boom and an arm rotatably connected with the upper turning body, and options, such as a bucket and a breaker, attached to an end of the arm, and the excavator needs to be able to exert large force when performing the operations, so that oil pressure is mainly used.
The excavator using oil pressure includes an engine providing power, a pump supplying oil to a cylinder connected to each actuator, and a value determining oil supplied to each cylinder.
When the cylinder is desired to be operated at a speed corresponding to an operation of a joystick by a user, only a predetermined oil needs to pass through the cylinder by generating a difference in pressure between a pump and a cylinder generated by a valve spool, and the oil is inevitably lost due to a difference in pressure between front and rear ends of the valve. The loss of the oil at the valve is the biggest reason for losing the entire oil pressure of the excavator, so that the loss of the oil pressure may be decreased by excluding a use of the valve spool, directly controlling oil of the pump, and supplying the oil to the cylinder.
That is, when the pump is directly controlled, the valve spool is not used, and thus oil of the pump at the same pressure cannot be appropriately distributed to each cylinder, so that one pump needs to be connected to one cylinder. However, the number of pumps may be limited due to a limit of an internal space of a vehicle. When the number of pumps is limited as described above, a logic valve for assigning a pump to each cylinder according to an operation of a joystick case by case may be used.